Problems associated with ground and surface water and below grade structures are well known. Such structures as below-grade foundation walls or highway or landscaping retaining walls are subject to hydrostatic pressure from ground water and surface water. If the water level rises in the soil outside of a foundation wall for example, hydrostatic pressure will be exerted on the wall and the floor enclosed by the foundation wall as the water attempts to rise to the same level inside of the foundation as the level outside. If the water cannot get through the floor and wall, the hydrostatic pressure exerted on both the floor and wall causes increased loading and deflection on both the wall and floor which may have not been designed for such loading. Moreover, leakage can occur through any cracks, joints or irregularities in the wall and the foundation footings, and if the hydrostatic pressure is not relieved, it eventually will penetrate up through cracks and joints in the floor and walls and into the interior of the structure. To design walls and floors for residential foundations and basements sufficiently strong so as to resist this hydrostatic pressure is usually not practical because of the cost. Therefore, there have been developed and are known methods for preventing the build up of hydrostatic pressure from ground and surface water.
One of the most common and cost effective ways to relieve hydrostatic pressure is to install drains around the foundation walls at or above the footings and connect these drains to a sump system. These drains commonly are perforated pip which are then surrounded with a layer of drainage aggregate to prevent the soil from plugging the drainage openings in the pipe. However, these drainage tiles can become overloaded from excess surface water which cannot filter down through the soil. This is especially true where there is a high ground water level and thus the surface water cannot continue to drain down through the soil.
In an effort to improve these drainage systems, there are known a number of different products and systems. One commonly used system is to apply to the exterior of the foundation wall a membrane usually made of high density polyethylene. The membrane is typically spaced from the wall and anchored to the foundation wall in a variety of ways. Depending upon the particular installation, these membranes may be sealed or not sealed, but they do provide a gap which serves as a drainage corridor should the membrane be punctured. In either event, the membrane provides a barrier to keep the water and thus the hydrostatic pressure from the foundation wall. In some installations, filter strips can be added by spacing the strips along the soil-side of the membranes, which strips will absorb surface water and carry it downwardly into the drainage aggregate surrounding the drain pipe.
Other variations of the membrane system are to apply a fabric backing to the membrane that contacts the wall to absorb moisture from the wall. In these installations, the membrane is sealed to provide an air corridor between it and the wall, but if the membrane is punctured, the system is rendered less effective.
There are also known and used insulated drainage boards or panels which are solid layers of material placed against the exterior of the foundation wall. These drainage panels typically have a layer of filter fabric in contact with the wall, a drainage board layer which absorbs and carries moisture and a vapor retarder on the exterior of the panels. These solid panels have the advantage that they will not puncture or deform during backfilling operations, and they also have insulating value.
However, all of the known products and methods use materials that are quite expensive and require considerable labor to install. As a result, most residential contractors, to keep the price of their houses competitive, will not use these improved drainage systems. Because of their relatively high cost, these prior art systems are principally used in building structures where they are specified by the owner or architect, or in commercial installations where the added cost is not a major factor.
In addition, many of these prior art products are not resistant to a number of petroleum based products which are frequently used as waterproofing or damp proofing materials on the exterior of the foundation before the application of the drainage systems. Not infrequently, the composition of the surrounding soil may have a deteriorating effect over a period of time on the materials, thus shortening their useful life.
There is therefore a need for an improved drainage system that is not only effective but low in cost so that it can be used for residential as well as other more costly structures without adding much to the cost of construction.
There is a further need for an improved drainage system that is easy to install, can be installed by unskilled labor, and which will not be adversely affected by backfilling operations, soil conditions, or waterproofing compounds.